U.S. patent application number 12/438071 was filed with the patent office on 2010-07-01 for blue phosphor, light-emitting device, and plasma display panel.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Yayoi Kitamura, Kojiro Okuyama, Masahiro Sakai, Seigo Shiraishi.
Application Number | 20100164360 12/438071 |
Document ID | / |
Family ID | 40093319 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100164360 |
Kind Code |
A1 |
Kitamura; Yayoi ; et
al. |
July 1, 2010 |
BLUE PHOSPHOR, LIGHT-EMITTING DEVICE, AND PLASMA DISPLAY PANEL
Abstract
The present invention provides a phosphor having high luminance,
a property of low luminance degradation during driving of a
light-emitting device and manufacturing processes, and chromaticity
y in PDP comparable to that of BAM:Eu. The present invention is the
phosphor represented by the general formula
xSrO.yEuO.MgO.zSiO.sub.2 where 2.970.ltoreq.x.ltoreq.3.500,
0.001.ltoreq.y.ltoreq.0.030, and 1.900.ltoreq.z.ltoreq.2.100 are
satisfied, wherein a main peak is present in the range of
diffraction angle 2.theta.=16.1 to 16.5 degree in the X-ray
diffraction pattern obtained by measurement on the blue phosphor
using an X-ray with a wavelength of 0.774 .ANG., and at least one
condition of the following conditions (A1) and (A2) is satisfied:
(A1) at least two peaks whose tops are located in the range of
diffraction angle 2.theta.=15.3 to 16.1 degree are present; and
(A2) at least two peaks whose tops are located in the range of
diffraction angle 2.theta.=22.2 to 23.3 degree are present.
Inventors: |
Kitamura; Yayoi; (Osaka,
JP) ; Shiraishi; Seigo; (Osaka, JP) ; Okuyama;
Kojiro; (Nara, JP) ; Sakai; Masahiro; (Kyoto,
JP) |
Correspondence
Address: |
HAMRE, SCHUMANN, MUELLER & LARSON P.C.
P.O. BOX 2902
MINNEAPOLIS
MN
55402-0902
US
|
Assignee: |
PANASONIC CORPORATION
Kadoma-shi, Osaka
JP
|
Family ID: |
40093319 |
Appl. No.: |
12/438071 |
Filed: |
March 28, 2008 |
PCT Filed: |
March 28, 2008 |
PCT NO: |
PCT/JP2008/000810 |
371 Date: |
February 19, 2009 |
Current U.S.
Class: |
313/486 ;
252/301.4R |
Current CPC
Class: |
C09K 11/7734 20130101;
H01J 11/12 20130101; H01J 11/42 20130101 |
Class at
Publication: |
313/486 ;
252/301.4R |
International
Class: |
H01J 17/49 20060101
H01J017/49; C09K 11/79 20060101 C09K011/79 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2007 |
JP |
2007-153287 |
Claims
1. A blue phosphor represented by the general formula
xSrO.yEuO.MgO.zSiO.sub.2 where 2.970.ltoreq.x.ltoreq.3.500,
0.001.ltoreq.y.ltoreq.0.030, and 1.900.ltoreq.z.ltoreq.2.100 are
satisfied, wherein a main peak is present in the range of
diffraction angle 2.theta.=16.1 to 16.5 degree in the X-ray
diffraction pattern obtained by measurement on the blue phosphor
using an X-ray with a wavelength of 0.774 .ANG., and at least one
condition of the following conditions (A1) and (A2) is satisfied:
(A1) at least two peaks whose tops are located in the range of
diffraction angle 2.theta.=15.3 to 16.1 degree are present; and
(A2) at least two peaks whose tops are located in the range of
diffraction angle 2.theta.=22.2 to 23.3 degree are present.
2. The blue phosphor according to claim 1, wherein both of the
conditions (A1) and (A2) are satisfied.
3. The blue phosphor according to claim 1, wherein
2.982.ltoreq.x.ltoreq.2.999, 0.001.ltoreq.y.ltoreq.0.018, and
1.980.ltoreq.z.ltoreq.2.020 are satisfied.
4. A blue phosphor represented by the general formula
xSrO.yEuO.MgO.zSiO.sub.2 where 2.970.ltoreq.x.ltoreq.3.500,
0.001.ltoreq.y.ltoreq.0.030, and 1.900.ltoreq.z.ltoreq.2.100 are
satisfied, wherein a main peak is present in the range of
diffraction angle 2.theta.=16.1 to 16.5 degree in the X-ray
diffraction pattern obtained by measurement on the blue phosphor
using an X-ray with a wavelength of 0.774 .ANG., and at least one
condition of the following conditions (B1) and (B2) is satisfied:
(B1) a peak or a group of peaks consisting of overlapping peaks
whose top is or tops are located in the range of diffraction angle
2.theta.=15.3 to 16.1 degree is present, and the one-tenth value
width of the peak or the group of peaks is not less than 0.13
degree and not more than 0.9 degree; and (B2) a peak or a group of
peaks consisting of overlapping peaks whose top is or tops are
located in the range of diffraction angle 2.theta.=22.2 to 23.3
degree is present, and the one-tenth value width of the peak or the
group of peaks is not less than 0.18 degree and not more than 1.5
degree.
5. The blue phosphor according to claim 4, wherein both of the
conditions (B1) and (B2) are satisfied.
6. The blue phosphor according to claim 4, wherein
2.982.ltoreq.x.ltoreq.2.999, 0.001.ltoreq.y.ltoreq.0.018, and
1.980.ltoreq.z.ltoreq.2.020 are satisfied.
7. A light-emitting device comprising a phosphor layer containing
the phosphor according to claim 1.
8. The light-emitting device according to claim 7, which is a
plasma display panel.
9. The light-emitting device according to claim 8, wherein the
plasma display panel comprises: a front panel; a back panel that is
arranged to face the front panel; barrier ribs that define the
clearance between the front panel and the back panel; a pair of
electrodes that are disposed on the back panel or the front panel;
an external circuit that is connected to the electrodes; a
discharge gas that is present at least between the electrodes and
contains xenon that generates a vacuum ultraviolet ray by applying
a voltage between the electrodes through the external circuit; and
phosphor layers that emit visible light induced by the vacuum
ultraviolet ray, the phosphor layers include a blue phosphor layer,
and the blue phosphor layer includes the blue phosphor.
Description
TECHNICAL FIELD
[0001] The present invention relates to a blue phosphor, and a
light-emitting device such as a plasma display panel (hereinafter
referred to as PDP).
BACKGROUND ART
[0002] Various aluminate phosphors have been put to practical use
as phosphors for energy-saving fluorescent lamps. As a blue
phosphor, for example, (Ba,Sr)MgAl.sub.10O.sub.17:Eu (BAM:Eu) is
mentioned. As a green phosphor, for example,
CeMgAl.sub.11O.sub.19:Tb, BaMgAl.sub.10O.sub.17:Eu,Mn, and the like
are mentioned.
[0003] In recent years, BAM:Eu, which has high luminance under
vacuum-ultraviolet excitation, has been used as a blue phosphor for
a PDP.
[0004] However, when a light-emitting device using the blue
phosphor BAM:Eu is driven for a long period, the luminance is
degraded significantly. Hence, in the light-emitting device use,
particularly in the PDP use, there is a strong demand for a
phosphor that shows less luminance degradation even after the
long-time driving.
[0005] On the other hand, methods using certain types of silicate
phosphors for a light-emitting device are proposed. For example, JP
2003-132803 A and JP 2004-176010 A disclose methods using
(Sr.sub.1-a, Ba.sub.a).sub.3-dMgSi.sub.2O.sub.8:Eu.sub.d (where
0.ltoreq.a.ltoreq.1, 0.01.ltoreq.d.ltoreq.0.1). JP 2006-12770 A
discloses a method using M.sub.3-eMgSi.sub.2O.sub.8:Eu.sub.e (where
M is at least one element selected from the group consisting of Sr,
Ca and Ba, and 0.001.ltoreq.e.ltoreq.0.2). JP 2006-124644 A
discloses a method using 3M.sup.1O.mMgO.nSiO.sub.2 (where M.sup.1
is at least one element selected from the group consisting of Sr,
Ca, and Ba, and 1.ltoreq.m.ltoreq.1.5, 2.ltoreq.n.ltoreq.2.6,
3<m+n).
[0006] According to elaborate studies of the present inventors,
however, it has been found that in most cases in the light-emitting
devices using the above conventional phosphors, the phosphors can
not inhibit the degradation of luminance during driving while
maintaining the high luminance. In addition, when a phosphor in
which a Sr site is not replaced with Ba is used, the phosphor has
higher chromaticity y and worse color purity than those of the blue
phosphor BAM:Eu used in the current PDP. On the other hand, when a
phosphor in which a Sr site is replaced with Ba is used, the
luminance intensity of the phosphor drops significantly.
Furthermore, when the above conventional phosphor having a Sr site
is used, the degradation of luminance is significant during the
manufacturing processes of applying and firing the phosphor with an
organic binder. These constitute problems.
DISCLOSURE OF INVENTION
[0007] The present invention has achieved a solution to the above
conventional problems, and it is an object of the present invention
to provide a phosphor having high luminance, a property of low
luminance degradation during driving of a light-emitting device and
manufacturing processes, and chromaticity y in PDP comparable to
that of BAM:Eu. It is a further object of the present invention to
provide a long-life light-emitting device, particularly PDP, using
the above phosphor.
[0008] The first embodiment of the present invention is the blue
phosphor represented by the general formula
xSrO.yEuO.MgO.zSiO.sub.2 where 2.970.ltoreq.x.ltoreq.3.500,
0.001.ltoreq.y.ltoreq.0.030, and 1.900.ltoreq.z.ltoreq.2.100 are
satisfied,
[0009] wherein a main peak is present in the range of diffraction
angle 2.theta.=16.1 to 16.5 degree in the X-ray diffraction pattern
obtained by measurement on the blue phosphor using an X-ray with a
wavelength of 0.774 .ANG., and at least one condition of the
following conditions (A1) and (A2) is satisfied: [0010] (A1) at
least two peaks whose tops are located in the range of diffraction
angle 2.theta.=15.3 to 16.1 degree are present; and [0011] (A2) at
least two peaks whose tops are located in the range of diffraction
angle 2.theta.=22.2 to 23.3 degree are present.
[0012] The second embodiment of the present invention is the blue
phosphor represented by the general formula
xSrO.yEuO.MgO.zSiO.sub.2 where 2.970.ltoreq.x.ltoreq.3.500,
0.001.ltoreq.y.ltoreq.0.030, and 1.900.ltoreq.z.ltoreq.2.100 are
satisfied,
[0013] wherein a main peak is present in the range of diffraction
angle 2.theta.=16.1 to 16.5 degree in the X-ray diffraction pattern
obtained by measurement on the blue phosphor using an X-ray with a
wavelength of 0.774 .ANG., and at least one condition of the
following conditions (B1) and (B2) is satisfied: [0014] (B1) a peak
or a group of peaks consisting of overlapping peaks whose top is or
tops are located in the range of diffraction angle 2.theta.=15.3 to
16.1 degree is present, and the one-tenth value width of the peak
or the group of peaks is not less than 0.13 degree and not more
than 0.9 degree; and [0015] (B2) a peak or a group of peaks
consisting of overlapping peaks whose top is or tops are located in
the range of diffraction angle 2.theta.=22.2 to 23.3 degree is
present, and the one-tenth value width of the peak or the group of
peaks is not less than 0.18 degree and not more than 1.5
degree.
[0016] Another embodiment of the present invention is a
light-emitting device including a phosphor layer containing the
above blue phosphor, and a preferable example of the light-emitting
device is a plasma display panel.
[0017] This plasma display panel includes, for example, a front
panel; a back panel that is arranged to face the front panel;
barrier ribs that define the clearance between the front panel and
the back panel; a pair of electrodes that are disposed on the back
panel or the front panel; an external circuit that is connected to
the electrodes; a discharge gas that is present at least between
the electrodes and contains xenon that generates a vacuum
ultraviolet ray by applying a voltage between the electrodes
through the external circuit; and phosphor layers that emit visible
light induced by the vacuum ultraviolet ray. The phosphor layers
include a blue phosphor layer, and the blue phosphor layer includes
the present phosphor.
[0018] According to the present invention, a phosphor that has good
luminance and chromaticity and shows less luminance degradation
during driving and manufacturing processes is provided. A long-life
light-emitting device such as a PDP that has good luminance and
chromaticity and shows less luminance degradation during the
long-time driving is provided.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a schematic cross-sectional perspective view
showing one example of a structure of the PDP of the present
invention.
[0020] FIG. 2 shows X-ray diffraction spectra in the range of
2.theta.=0 to 60 degree of the Example 5 of the present invention
and Comparative Example 2.
[0021] FIG. 3 shows X-ray diffraction spectra in the range of
2.theta.=15.3 to 16.5 degree of the Example 5 of the present
invention and Comparative Example 2.
[0022] FIG. 4 shows X-ray diffraction spectra in the range of
2.theta.=22.2 to 23.3 degree of the Example 5 of the present
invention and Comparative Example 2.
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] Hereinafter, embodiments of the present invention will be
described in detail.
<Composition of Phosphor>
[0024] The blue phosphor of the present invention is represented by
the general formula xSrO.yEuO.MgO.zSiO.sub.2 (where
2.970.ltoreq.x.ltoreq.3.500, 0.001.ltoreq.y.ltoreq.0.030,
1.900.ltoreq.z.ltoreq.2.100). With respect to x, y and z,
preferable ranges are 2.982.ltoreq.x.ltoreq.2.999,
0.001.ltoreq.y.ltoreq.0.018, and 1.980.ltoreq.z.ltoreq.2.020,
respectively. z is preferably 2.00.
<Characteristics Relating to X-Ray Diffraction of
Phosphor>
[0025] The blue phosphor of the present invention is characterized
in that a main peak is present in the range of diffraction angle
2.theta.=16.1 to 16.5 degree in the X-ray diffraction pattern
obtained by measurement on the blue phosphor using an X-ray with a
wavelength of 0.774 .ANG., and at least two peaks whose tops are
located in the certain range of diffraction angle 2.theta. are
present (condition A). Alternatively, a main peak is present in the
range of diffraction angle 2.theta.=16.1 to 16.5 degree, as well as
a peak or a group of peaks consisting of overlapping peaks whose
top is or tops are located in the certain range of diffraction
angle 2.theta. is present, and the one-tenth value width of the
peak or the group of peaks falls in the certain range (condition
B).
[0026] The present inventors have found from elaborate studies
based on the experimental results that the blue phosphor that has
the above composition and satisfies the above condition A or
condition B is a phosphor that has good luminance, good
chromaticity and a high luminance retaining rate. With respect to
the conventional silicate blue phosphor represented by the general
formula xSrO.yEuO.MgO.zSiO.sub.2, the number of peak whose top is
located in the above range of diffraction angle 2.theta. is one,
and the one-tenth value width of the peak is outside the above
range. The reason why the blue phosphor satisfying the above
condition A or condition B has excellent light-emitting properties
is not clear but assumed to be as follows.
[0027] With respect to the conventional silicate blue phosphor, the
(one) peak whose top is located in the range of diffraction angle
2.theta.=15.3 to 16.1 degree corresponds to lattice spacing d=2.80
.ANG. and it is composed mainly of overlap of a peak with a plane
index (h, k, l)=(-4, 0, 2) and a peak with a plane index (h, k,
l)=(4, 1, 1). The (one) peak whose top is located in the range of
diffraction angle 2.theta.=22.2 to 23.3 degree corresponds to
lattice spacing d=1.95 .ANG. and it is composed mainly of overlap
of a peak with a plane index (h, k, l)=(-4, 2, 2) and a peak with a
plane index (h, k, l)=(4, 0, 4). In addition, plane indices of
peaks that overlap the above peaks further exist in theory. For the
peak whose top is located in the range of diffraction angle
2.theta.=15.3 to 16.1 degree, a plane index (h, k, l)=(-4, 1, 1)
and a plane index (h, k, l)=(4, 0, 2) also exist. For the peak
whose top is located in the range of diffraction angle
2.theta.=22.2 to 23.3 degree, a plane index (h, k, l)=(-4, 0, 4)
and a plane index (h, k, l)=(4, 2, 2) also exist. Furthermore,
besides these there are plane indices for neighboring peaks. In the
experiments of the present inventors, firing under the unique
condition is employed as described later so as to obtain the
phosphor that satisfies the condition A or condition B. It is
considered that the lattice constant of the phosphor and positions
of the peaks with the above plane indices vary by this firing,
which results in an increase in the peak number or appearance of
the group of peaks having the certain one-tenth value width. As a
result, it is considered that the light-emitting property
(luminance retaining rate) of the phosphor is improved. In the
present invention, the change of the peak shapes is mainly
according to the above condition A or condition B, and does not
involve a change of all peaks. Therefore, it is considered that it
is caused not merely by the degraded crystallinity, but by the
change of the crystalline structure of the silicate blue
phosphor.
[0028] In the present invention, "a main peak is present in the
range of diffraction angle 2.theta.=16.1 to 16.5 degree" means that
a peak having a highest intensity is present in the range of
diffraction angle 2.theta.=16.1 to 16.5 degree in the X-ray
diffraction pattern measured in the range of diffraction angle
2.theta.=5 to 45 degree using an X-ray with a wavelength of 0.774
.ANG..
[0029] In the condition A, it is required that a main peak is
present in the range of diffraction angle 2.theta.=16.1 to 16.5
degree and that at least one condition of the following conditions
(A1) and (A2) is satisfied; [0030] (A1) At least two peaks whose
tops are located in the range of diffraction angle 2.theta.=15.3 to
16.1 degree are present; and [0031] (A2) At least two peaks whose
tops are located in the range of diffraction angle 2.theta.=22.2 to
23.3 degree are present.
[0032] In the condition A, it is preferable that both of the
conditions (A1) and (A2) are satisfied.
[0033] In the present invention, in order to distinguish a peak
from a change of signal intensity by noise and the like, among the
changes of signal intensity, a change of signal intensity having an
intensity of 1/20 or more of main peak present in the range of 16.1
to 16.5 degree is recognized as a peak. In the present invention,
"two peaks are present" means the case where a sign of the
differential values at each angle point constituting the spectrum
reverses three times within the predetermined range of diffraction
angle, while ignoring noise. Therefore, here, even when two peaks
overlap so as to constitute one bimodal peak, it is recognized as
"two peaks are present". The case where three peaks are present
should be handled in the same way.
[0034] In the condition B, it is required that a main peak is
present in the range of diffraction angle 2.theta.=16.1 to 16.5
degree and that at least one condition of the following conditions
(B1) and (B2) is satisfied: [0035] (B1) a peak or a group of peaks
consisting of overlapping peaks whose top is or tops are located in
the range of diffraction angle 2.theta.=15.3 to 16.1 degree is
present, and the one-tenth value width of the peak or the group of
peaks is not less than 0.13 degree and not more than 0.9 degree;
and [0036] (B2) a peak or a group of peaks consisting of
overlapping peaks whose top is or tops are located in the range of
diffraction angle 2.theta.=22.2 to 23.3 degree is present, and the
one-tenth value width of the peak or the group of peaks is not less
than 0.18 degree and not more than 1.5 degree.
[0037] In the condition B, it is preferable that both of the
conditions (B1) and (B2) are satisfied. In the condition (B1), the
one-tenth value width of the peak or the group of peaks is
preferably not less than 0.13 degree and not more than 0.60 degree,
and more preferably not less than 0.13 degree and not more than
0.40 degree. In the condition (B2), the one-tenth value width of
the peak or the group of peaks is preferably not less than 0.18
degree and not more than 0.80 degree, and more preferably not less
than 0.18 degree and not more than 0.60 degree.
[0038] Here, the one-tenth value width is defined as the full width
of a peak at a height one-tenth of a peak intensity. In addition,
here, a peak having a so-called shoulder is taken as one peak.
Furthermore, two or more of peaks (a group of peaks) may appear in
the range of diffraction angle 2.theta.=15.3 to 16.1 degree and
22.2 to 23.3 degree in some case. In this case, peaks constituting
a group normally appear overlapping each other. In this case, with
respect to the condition B, the one-tenth value width is determined
assuming that the whole of a group of peaks (two or more of
overlapping peaks) is taken as one peak without dividing the group
of peaks into each peak. In addition, the highest value of peak
intensity among the values of intensities of peaks constituting the
group is employed as the value of peak intensity of the group of
peaks.
[0039] With respect to the group of peaks, "peak tops are located
in the range of diffraction angle 2.theta.=15.3 to 16.1 degree"
means the case where every top of the peaks constituting a group is
located in the range of diffraction angle 2.theta.=15.3 to 16.1
degree. The same is applied to "peak tops are located in the range
of diffraction angle 2.theta.=22.2 to 23.3 degree" in the condition
(B2).
<Powder X-Ray Diffraction Measurement>
[0040] Next, a powder X-ray diffraction measurement on the blue
phosphor of the present invention will be described.
[0041] For the powder X-ray diffraction measurement, for example,
BL19B2 powder X-ray diffraction equipment (Debye-Scherrer optical
system using an imaging plate; hereinafter referred to as BL19
diffraction equipment) in the large-scale synchrotron radiation
facility, SPring 8 is used. Phosphor powder is packed tightly into
a Lindemann glass capillary with an internal diameter of 200 .mu.m.
The incident X-ray wavelength is set to approximately 0.774 .ANG.
using a monochromator. While a sample is spun using a goniometer, a
diffraction intensity is recorded on an imaging plate. The
measuring time is to be determined, paying attention to keep the
imaging plate unsaturated. The measuring time is, for example, 5
minutes. The imaging plate is developed and an X-ray diffraction
spectrum is read out.
[0042] It should be noted that an error from the zero point when
the data is read out from the developed imaging plate is
approximately 0.03 in terms of diffraction angle 2.theta..
[0043] It should be noted that an accurate incident X-ray
wavelength is confirmed using a CeO.sub.2 powder (SRM No. 674a) of
NIST (National Institute of Standards and Technology) whose lattice
constant is 5.4111 .ANG.. Rietveld analysis on the data measured on
the CeO.sub.2 powder is carried out while varying the lattice
constant (a axis length). The actual X-ray wavelength .lamda. is
calculated based on the difference between the value a' obtained
for the predetermined X-ray wavelength .lamda.' and the actual
value (a=5.4111 .ANG.) from the following formula.
.lamda.=a.lamda.'/a'
[0044] For the Rietveld analysis, RIETAN-2000 program (Rev. 2.3.9
or later; hereinafter referred to as RIETAN) is used (see NAKAI
Izumi, IZUMI Fujio, "Funmatsu X-sen kaiseki-no-jissai--Rietveld hou
nyumon" (Practice of powder X-ray analysis--introduction to
Rietveld method), Discussion Group of X-Ray Analysis, the Japan
Society for Analytical Chemistry, Asakura Publishing, 2002, and
http://homepage.mac.com/fujioizumi/).
[0045] It should be noted that X-ray diffraction is a phenomenon
that is observed when crystal lattice, incidence of X-ray, and
geometric arrangement of diffraction satisfy the Bragg's
condition:
2d sin .theta.=n.lamda..
Though the observation of the spectrum is possible using general
X-ray diffractometers, the diffraction profile observed has some
differences because the observed strength depends on the incident
X-ray wavelength.
<Manufacture Method of Phosphor>
[0046] Hereinafter, the method of manufacturing the phosphor of the
present invention will be described below. The method of
manufacturing the phosphor of the present invention is not limited
to the method described below.
[0047] As a strontium source material, a strontium compound that
can be converted into strontium oxide by firing, such as strontium
hydroxide, strontium carbonate, strontium nitrate, strontium
halide, and strontium oxalate, each having high purity (purity of
99% or more), may be used. Strontium oxide having high purity
(purity of 99% or more) also may be used.
[0048] As a magnesium source material, a magnesium compound that
can be converted into magnesium oxide by firing, such as magnesium
hydroxide, magnesium carbonate, magnesium nitrate, magnesium
halide, magnesium oxalate, and basic magnesium carbonate, each
having high purity (purity of 99% or more), may be used. Magnesium
oxide having high purity (purity of 99% or more) also may be
used.
[0049] As a europium source material, a europium compound that can
be converted into europium oxide by firing, such as europium
hydroxide, europium carbonate, europium nitrate, europium halide,
and europium oxalate, each having high purity (purity of 99% or
more), may be used. Europium oxide having high purity (purity of
99% or more) also may be used.
[0050] As a silicon source material, various source materials that
can be converted into oxides may be used in the same way.
[0051] The method for mixing the source materials may be wet mixing
in a solution or dry mixing of dry powders. A ball mill, a stirred
media mill, a planetary mill, a vibration mill, a jet mill, a
V-type mixer, an agitator, and the like, which are in general
industrial use, may be used. Since coarse particles in the source
materials adversely affect the light-emitting property, it is
preferable that the particles are classified to improve particle
size uniformity.
[0052] Next, a phosphor is obtained by firing the mixed powder at
1000.degree. C. to 1300.degree. C. for 2 to 8 hours under a weakly
reducing atmosphere in which partial pressure of oxygen is
adjusted. It should be noted that the firing temperature has to be
adjusted appropriately depending on the classification condition.
The partial pressure of oxygen may be -15 to -7 in terms of
log(PO2/atm). Here, "PO2/atm" means "a value of partial pressure of
oxygen expressed in atm unit", and log is a common logarithm.
[0053] As a furnace to be used for the firing, furnaces that are in
general industrial use may be used. A gas furnace or an electric
furnace of the batch type or continuous type such as a pusher
furnace may be used.
[0054] When a hydroxide, a carbonate, a nitrate, a halide, an
oxalate or the like that can be converted into oxide by firing is
used as a source material, it is preferable that pre-firing is
carried out before main firing. The pre-firing may be carried out
in an air atmosphere, but should be carried out at a temperature
lower than that of the main firing by about 150.degree. C.
[0055] Then, the obtained phosphor powder is fired at 300 to
600.degree. C. for 1 to 5 hours under the atmosphere in which a
concentration of an organic gas is adjusted. The phosphor of the
present invention, which satisfies the above condition A and/or
condition B, can be obtained by this firing. As the organic gas,
butane and octane can be used, and it is presumed that a gas of
molecules composed of a carbon atom and a hydrogen atom, such as
methane, ethane, or propane, can be used similarly. The
concentration of the organic gas may be 5 to 1000 ppm.
[0056] Alternatively, the phosphor obtained by the above firing
under the atmosphere in which the partial pressure of oxygen is
adjusted is fired with an organic compound at 300 to 600.degree. C.
for 1 to 5 hours. The phosphor of the present invention, which
satisfies the above condition A and/or condition B, can be obtained
also by this firing. As the organic compound, ethyl cellulose can
be used, and it is presumed that other cellulose resins, acrylic
resins, or urethane resins can be used similarly. In order to mix
these organic compound species evenly with the phosphor, solvents
such as monovalent alcohols having a high boiling point,
multivalent alcohols, and compounds obtained by etherifying and/or
esterifying alcohols can be used. The amount of the organic
compound to be used may be 0.05 to 1.0 g relative to 1 g of the
phosphor.
[0057] The particle size distribution and flowability of the
phosphor powder can be adjusted by crushing the obtained phosphor
powder again using a ball mill, a jet mill, or the like, and
further by washing or classifying it, if necessary.
<Uses of Phosphor>
[0058] A light-emitting device having good luminance, chromaticity
and luminance retaining rate can be constructed by applying the
phosphor of the present invention to a light-emitting device having
a phosphor layer. Specifically, for a light-emitting device having
a phosphor layer in which BAM:Eu is used, all or part of BAM:Eu is
replaced with the phosphor of the present invention, while a
light-emitting device may be constructed according to a known
method. It is possible to construct a light-emitting device in
which the phosphor of the present invention and a light-emitting
diode (LED) chip are used in combination. Examples of the
light-emitting device include a PDP, a fluorescent panel, and a
fluorescent lamp, and among them, a PDP is suitable.
[0059] Hereinafter, an embodiment (the PDP of the present
invention) in which the blue phosphor of the present invention is
applied to a PDP will be described with an example of an AC
surface-discharge type PDP. FIG. 1 is a cross-sectional perspective
view showing a principal structure of an AC surface-discharge type
PDP 10. It should be noted that the PDP shown here is illustrated
for convenience' sake with a size that is appropriate for a
specification of 1024.times.768 pixels, which is 42-inch class, and
the present invention may be applied to other sizes and
specifications as well.
[0060] As illustrated in FIG. 1, this PDP 10 includes a front panel
20 and a back panel 26, and these panels are arranged with their
main surfaces facing each other.
[0061] The front panel 20 includes a front panel glass 21 as a
front substrate, strip-shaped display electrodes (X-electrode 23,
Y-electrode 22) provided on one main surface of the front panel
glass 21, a front-side dielectric layer 24 having a thickness of
about 30 .mu.m covering the display electrodes, and a protective
layer 25 having a thickness of about 1.0 .mu.m provided on the
front-side dielectric layer 24.
[0062] The above display electrode includes a strip-shaped
transparent electrode 220 (230) having a thickness of 0.1 .mu.m and
a width of 150 .mu.m, and a bus line 221 (231) having a thickness
of 7 .mu.m and a width of 95 .mu.m and laid on the transparent
electrode. A plurality of pairs of the display electrodes are
disposed in the y-axis direction, where the x-axis direction is a
longitudinal direction.
[0063] Each pair of display electrodes (X-electrode 23, Y-electrode
22) is connected electrically to a panel drive circuit (not shown)
in the vicinity of the ends of the width direction (y-axis
direction) of the front panel glass 21. It should be noted that the
Y-electrodes 22 are connected collectively to the panel drive
circuit and the X-electrodes 23 each are connected independently to
the panel drive circuit. When the Y-electrodes 22 and the certain
X-electrodes 23 are fed using the panel drive circuit, a surface
discharge (sustained discharge) is generated in the gap
(approximately 80 .mu.m) between the X-electrode 23 and the
Y-electrode 22. The X-electrode 23 also can operate as a scan
electrode, and in this case, a write discharge (address discharge)
can be generated between the X-electrode 23 and an address
electrode 28 to be described later.
[0064] The above-mentioned back panel 26 includes a back panel
glass 27 as a back substrate, a plurality of address electrodes 28,
a back-side dielectric layer 29, barrier ribs 30, and phosphor
layers 31 to 33, each of which corresponds to one color of red (R),
green (G), and blue (B). The phosphor layers 31 to 33 are provided
so that they contact with side walls of two adjacent barrier ribs
30 and with the back-side dielectric layer 29 between the adjacent
barrier ribs 30, and repeatedly disposed in sequence in the x-axis
direction.
[0065] The blue phosphor layer (B) contains the above-mentioned
blue phosphor of the present invention. It should be noted that the
blue phosphor of the present invention may be used singularly or
several kinds of the blue phosphor of the present invention may be
mixed. Moreover, the blue phosphor of the present invention may be
used as a mixture with a known phosphor such as BAM:Eu. On the
other hand, the red phosphor layer and the green phosphor layer
contain commonly-used phosphors. Examples of a red phosphor include
(Y,Gd)BO.sub.3:Eu and Y.sub.2O.sub.3:Eu, and examples of a green
phosphor include Zn.sub.2SiO.sub.4:Mn, YBO.sub.3:Tb, and
(Y,Gd)BO.sub.3:Tb.
[0066] Each phosphor layer can be formed by applying a phosphor ink
in which phosphor particles are dissolved to the barrier ribs 30
and the back-side dielectric layer 29 by a known applying method
such as a meniscus method and a line jet method, and drying and
firing them (e.g., at 500.degree. C., for 10 minutes). The
above-mentioned phosphor ink can be prepared, for example, by
mixing 30% by mass of the blue phosphor having a volume average
particle diameter of 2 .mu.m, 4.5% by mass of ethyl cellulose with
a mass average molecular weight of about 200,000, and 65.5% by mass
of butyl carbitol acetate. In this regard, it is preferable that
the viscosity thereof is adjusted eventually to about 2000 to 6000
cps (2 to 6 Pas), because the adherence of the ink to the barrier
ribs 30 can be enhanced.
[0067] The address electrodes 28 are provided on the one main
surface of the back panel glass 27. The back-side dielectric layer
29 is provided so as to cover the address electrodes 28. The
barrier ribs 30 have a height of about 150 .mu.m and a width of
about 40 .mu.m, and the longitudinal direction is in the y-axis
direction. The barrier ribs 30 are provided on the back-side
dielectric layer 29 so as to correspond to the pitch of the
adjacent address electrodes 28.
[0068] Each of the address electrodes 28 has a thickness of 5 .mu.m
and a width of 60 .mu.m. A plurality of address electrodes 28 are
disposed in the x-axis direction, where the y-axis direction is a
longitudinal direction. The address electrodes 28 are disposed at a
certain pitch (about 150 .mu.m). A plurality of address electrodes
28 each are connected independently to the above-mentioned panel
drive circuit. Address discharge can be generated between a certain
address electrode 28 and a certain X-electrode 23 by feeding each
address electrode individually.
[0069] The front panel 20 and the back panel 26 are disposed so
that the address electrode 28 and the display electrode are
orthogonal to each other. The peripheral portions of both the
panels 20 and 26 are bonded and sealed with a frit glass sealing
portion (not shown) that serves as a sealing member.
[0070] An enclosed space between the front panel 20 and the back
panel 26, which has been bonded and sealed with the frit glass
sealing portion, is filled with a discharge gas composed of a rare
gas such as He, Xe and Ne at a predetermined pressure (ordinarily
about 6.7.times.10.sup.4 to 1.0.times.10.sup.5 Pa).
[0071] It should be noted that a space corresponding to a space
between two adjacent barrier ribs 30 is a discharge space 34. A
region where a pair of display electrodes and one address electrode
28 intersect with the discharge space 34 in between corresponds to
a cell used for displaying images. It should be noted that in this
embodiment, the cell pitch in the x-axis direction is set to
approximately 300 .mu.m and the cell pitch in the y-axis direction
is set to approximately 675 .mu.m.
[0072] When the PDP 10 is driven, a sustained discharge is
generated by applying a pulse between a pair of the display
electrodes (X-electrode 23, Y-electrode 22) after an address
discharge is generated by applying a pulse voltage to the certain
address electrode 28 and the certain X-electrode 23 by the panel
drive circuit. The phosphors contained in the phosphor layers 31 to
33 are allowed to emit visible light using the ultraviolet ray with
a short wavelength (a resonance line with a central wavelength of
about 147 nm and a molecular beam with a central wavelength of 172
nm) thus generated. Thereby, a prescribed image can be displayed on
the front panel side.
[0073] The phosphor of the present invention can be applied to a
fluorescent panel including a fluorescent layer that is excited by
an ultraviolet ray and then emits light according to a known
manner. This fluorescent panel has good luminance as well as an
excellent resistance to luminance degradation compared to the
conventional fluorescent panels. This fluorescent panel can be
used, for example, as a backlight of a liquid crystal display
device.
[0074] The phosphor of the present invention can be applied also to
a fluorescent lamp (e.g., electrodeless fluorescent lamp, xenon
fluorescent lamp, fluorescent mercury lamp) according to a known
manner. This fluorescent lamp has good luminance as well as an
excellent resistance to luminance degradation compared to the
conventional fluorescent lamps.
[0075] Hereinafter, the embodiment of the present invention will be
described in detail giving Examples. It should be noted that the
present invention is not intended to be limited to the
Examples.
[0076] As starting materials, SrCO.sub.3, Eu.sub.2O.sub.3, MgO, and
SiO.sub.2 were used. These were weighed according to the
compositions shown in Table 1, and wet-mixed in pure water using a
ball mill. Since coarse particles in the source materials adversely
affect the light-emitting property, the particles were classified
to improve particle size uniformity.
[0077] After these mixtures were dried and pre-fired, they were
fired at 1000.degree. C. to 1300.degree. C. for 4 hours under a
weakly reducing atmosphere in which a partial pressure of oxygen is
adjusted, and the phosphors thus were obtained. The obtained
phosphor powders were fired further at 400.degree. C. for 1 hour
under the atmosphere in which an organic gas concentration was
adjusted or under the atmosphere containing an organic compound,
and the phosphor powders of Examples 1 to 8 thus were obtained.
[0078] On the other hand, after the raw materials were mixed
according to the predetermined compositions and dried similarly,
the mixtures were fired under the weakly reducing atmosphere at the
temperature shown in Table 3. The phosphor powders of Comparative
Examples 1 to 5 thus were obtained. In the phosphors of Comparative
Examples, the phosphors of Comparative Examples 1 to 3 differ from
those of Examples in the point that the phosphors of Comparative
Examples 1 to 3 had not experienced the firing process under the
atmosphere containing an organic gas or an organic compound.
<Powder X-Ray Diffraction Measurement>
[0079] The X-ray diffraction patterns of the phosphors of Examples
and Comparative Examples were measured by the above-mentioned
method, using BL19 diffraction equipment in the large-scale
synchrotron radiation facility, SPring 8. It should be noted that
the measuring time was set to 5 minutes.
<Measurement of Relative Luminance>
[0080] The measurement of luminance was carried out by irradiating
the phosphors with a vacuum ultraviolet ray with a wavelength of
146 nm under vacuum and measuring light-emission in the visible
region. The luminance is luminance Y in the XYZ color coordinate
system of International Commission on Illumination and was
evaluated as a value relative to the standard sample BAM:Eu
(Ba.sub.0.9MgAl.sub.10O.sub.17:Eu.sub.0.1).
<Panel Luminance and Luminance Retaining Rate>
[0081] PDPs having the structure of FIG. 1 were manufactured
according to the above-described embodiment of an AC
surface-discharge type PDP, using the blue phosphors of Examples
and Comparative Examples. The manufactured panels were subjected to
an accelerated driving test, and the degradation of luminance after
driving equivalent to 3000 hours driving from the initial luminance
was measured. The luminance retaining rate thus was determined. It
should be noted that the luminance is luminance Y in the XYZ color
coordinate system of International Commission on Illumination and
initial relative luminance was evaluated as a value relative to the
standard sample BAM:Eu
(Ba.sub.0.9MgAl.sub.10O.sub.17:Eu.sub.0.1).
<Relationship Among Composition, Crystal Structure, and
Luminance and Others>
[0082] Table 1 shows the compositions of the samples of Examples
and Comparative Examples (x, y, and z values of the general formula
xSrO.yEuO.MgO.zSiO.sub.2), the partial pressures of oxygen during
firing, the firing temperatures, and whether firing was carried out
under the atmosphere containing an organic gas or not. Table 2
shows the relationship among the one-tenth value width of a peak or
a peak of groups in the range of diffraction angle 2.theta.=15.3 to
16.1 degree and 2.theta.=22.2 to 23.3 degree and the number of the
peaks in the range of those diffraction angles, which were obtained
by the X-ray diffraction measurement of the samples of Examples and
Comparative Examples, and the relative luminance, the initial
luminance and the luminance retaining rate of the panel.
TABLE-US-00001 TABLE 1 xSrO.cndot.yEuO.cndot.MgO.cndot.zSiO.sub.2
Partial Firing pressure temper- Sample of ature Treat- number x y z
oxygen /.degree. C. ment Example 1 2.9955 0.0045 2.0000 High 1100
Yes Example 2 2.9955 0.0045 2.0000 Middle 1300 Yes Example 3 2.9925
0.0075 2.0000 Middle 1250 Yes Example 4 2.9886 0.0114 2.0000 Middle
1250 Yes Example 5 2.9874 0.0126 2.0000 Middle 1200 Yes Example 6
2.9990 0.0010 2.0000 Middle 1200 Yes Example 7 2.9820 0.0180 2.0000
Low 1300 Yes Example 8 2.9955 0.0045 1.9900 Middle 1200 Yes
Comparative 2.9895 0.0105 2.0000 Low 1150 Not Example 1 done
Comparative 2.9874 0.0126 2.0000 Middle 1250 Not Example 2 done
Comparative 2.9805 0.0195 2.0000 Middle 900 Not Example 3 done
Comparative 3.6000 0.0001 2.0000 High 1100 Yes Example 4
Comparative 2.9500 0.0500 2.0000 Low 900 Yes Example 5
TABLE-US-00002 TABLE 2 Panel luminance Initial Luminance One-tenth
value width Relative relative retaining 15.3-16.1 degree 22.2-23.3
degree Number of peak luminance luminance rate Sample number
/degree /degree 15.3-16.1 degree 22.2-23.3 degree /% /% /% Example
1 0.15 0.25 2 2 95 95 95 Example 2 0.13 0.18 2 2 94 101 96 Example
3 0.20 0.28 2 2 91 100 95 Example 4 0.26 0.38 2 2 95 105 100
Example 5 0.24 0.34 2 2 95 98 98 Example 6 0.14 0.20 2 2 93 105 99
Example 7 0.35 0.57 2 2 95 99 97 Example 8 0.16 0.28 2 2 91 102 95
Comparative 0.10 0.14 1 1 100 95 87 Example 1 Comparative 0.11 0.16
1 1 108 95 83 Example 2 Comparative 1.82 2.86 1 1 61 57 78 Example
3 Comparative 0.10 0.15 1 1 58 55 82 Example 4 Comparative 1.44
2.69 1 1 85 59 68 Example 5 Reference 100 100 85 (BAM: Eu)
[0083] It should be noted that in Table 1, the partial pressure of
oxygen "high" is log(PO2/atm)=about -12, "middle" is
log(PO2/atm)=about -13, and "low" is log(PO2/atm)=about -14. In
particular, as one example of Examples, in Example 3, the partial
pressure of oxygen was set to middle, butane was used as the
organic gas, and the concentration thereof was set to 100 ppm. In
Example 4, the partial pressure of oxygen was set to middle, and
40% by mass of the phosphor, 12% by mass of ethyl cellulose as the
organic compound species, and 48% by mass of terpineol as a solvent
were mixed and fired.
[0084] The values of chromaticity y of the samples of Examples 1 to
8 are comparable to that of the standard sample BAM:Eu.
[0085] As one example of the present invention, the X-ray
diffraction spectrum of Example 5 is shown in FIG. 2, and the
enlarged views of each angle range are shown in FIG. 3 and FIG. 4.
The X-ray diffraction spectra of Comparative Example 2 are also
shown as a comparative example.
[0086] When a blue phosphor in which all values of relative
luminance, initial relative luminance and a luminance retaining
rate of the panel are 90% or more is defined as a phosphor having
good luminance and an excellent luminance retaining rate, it can be
seen from Table 2 that phosphors having good luminance and an
excellent luminance retaining rate are obtained when at least two
peaks whose tops are located in the range of diffraction angle
2.theta.=15.3 to 16.1 degree and/or at least two peaks whose tops
are located in the range of diffraction angle 2.theta.=22.2 to 23.3
degree are present.
[0087] Furthermore, it can be seen from Table 2 that phosphors
having good luminance and an excellent luminance retaining rate are
obtained when a peak or a group of peaks consisting of overlapping
peaks whose top is or tops are located in the range of diffraction
angle 2.theta.=15.3 to 16.1 degree is present, and the one-tenth
value width of the peak or the group of peaks is not less than 0.13
degree and not more than 0.9 degree; and/or a peak or a group of
peaks consisting of overlapping peaks whose top is or tops are
located in the range of diffraction angle 2.theta.=22.2 to 23.3
degree is present, and the one-tenth value width of the peak or the
group of peaks is not less than 0.18 degree and not more than 1.5
degree.
[0088] It is considered that the change of lattice constant caused
by the above firing under the atmosphere containing an organic gas
leads to the increase in the number of peaks whose tops are located
in the above range of diffraction angle and the increase in the
one-tenth value width of the above peak or the above group of peaks
in Examples relative to Comparative Examples. It is also considered
that this change of lattice constant allows the phosphor to be in
the state in which the phosphor preliminarily is degraded without
causing the large decrease of luminance, and consequently the
luminance degradation is inhibited in the manufacturing process,
which results in the increase in the initial luminance and also
stability in the panel.
[0089] As for the composition, substantially,
2.982.ltoreq.x.ltoreq.2.999, 0.001.ltoreq.y.ltoreq.0.018, and
z=2.00 are preferable, judging from Table 1. However, it is
conceivable that the cases may occur in which Sr, Eu, and Si are
not incorporated actually in the crystal, or coexisting atoms which
have been mixed with the phosphor after the completion of the
phosphor has no adverse effects. Taking these cases into
consideration, in the present invention,
2.970.ltoreq.x.ltoreq.3.500, 0.001.ltoreq.y.ltoreq.0.030, and
1.900.ltoreq.z.ltoreq.2.100 should be allowable.
INDUSTRIAL APPLICABILITY
[0090] The phosphor of the present invention can be applied to
light-emitting devices, among them in particular, PDPs.
Furthermore, the phosphor of the present invention can be applied
to the use of fluorescent lamps such as an electrodeless
fluorescent lamp, a xenon fluorescent lamp, and a fluorescent
mercury lamp, fluorescent panels mainly used for a backlight of the
liquid crystal display device, and the like.
* * * * *
References